1. Field of the Invention
Conventional tennis racquets generally include a wood or steel frame with stringing mounted therein in a horizontal and vertical fashion. Normally the string is inserted at a desired maximum tension. However this tension slowly decreases over a period of usage of the racquet. Therefore a means of continually varying the adjustment of the tension of the strings at a given moment is desirable.
Also the strings of a normal tennis racquet are bent about very narrow bending angles and as such are completely prevented from any axial movement thereof. The present invention provides a system for using a non-endless string which allows axial movement of the string itself when the racquet surface contacts a ball. In other words when a ball is struck by the racquet surface certain strings will move axially in certain chosen directions and provide additional action during contact with the tennis ball to improve control and accuracy.
Also in conventionally strung tennis racquets the minimization of axial movement of the stringing leads to frequent breakage of the strings themselves whereas if a means to allow axial movement of the strings would be provided then this breaking of the strings due to an excess amount of pressure being exerted on a given string section would be minimized. The present invention provides a means for creating an adjustable tennis racquet with a non-endless string wherein an amount of such axial movement is existing.
2. Description of the Prior Art
Examples of patents of the prior art pertinent to the present invention are as follows:
U.S. Pat. Nos. 240,183; 1,131,418; 1,476,906; 1,667,450; 1,682,199; 1,750,727; 1,862,581; 1,937,787; 2,034,444; 2,089,118; 2,109,525; 2,145,785; 2,206,548; 2,274,788; 2,969,984; 3,078,098; 3,083,968; 3,431,626; 3,528,658; 3,568,290; 3,711,092; 3,724,850; 3,801,099; 3,834,699; 3,901,507; 3,930,648; 3,934,876; 3,948,519; 4,023,799; 4,026,553; and 4,057,249.
Foreign Patents
Australia Pat. No. 208,945 Australia Pat. No. 252,990 France Pat. No. 784,057 France Pat. No. 812,970 Great Britain Pat. No. 4305 Great Britain Pat. No. 380,915 Great Britain Pat. No. 5358 and Germany Pat. No. 811,932.
Of particular note is U.S. Pat. No. 4,057,249 recently issued to the same above-named inventors which discloses a similar system using a stringing which is axially movable by means of a plurality of sheaves mounted in the head area of the tennis racquet. That concept differs substantially from the present invention due to the usage in that patent of a single endless string. The present invention provides a means for achieving the desired full axial movement as has been achieved in the U.S. Pat. No. 4,057,249 however without using an endless string but using a connector member which is allowed lateral movement. It has been found that the use of the single non-endless string is more easy to manufacture as well as facilitating the initial tensioning and placement of the stringing. Also by the elimination of the rotatable tensioning roller 38 a possible source of breakage is eliminated.